For stubborn burnt food, add water and a couple of tablespoons of baking soda to the pan, bring it to a boil, and let it simmer for a few minutes. Once it cools a little, the burnt bits come away easily with a wooden spoon. For dark, greasy stains on the outside bottom, let the vessel cool completely, spread a thick baking soda paste over the marks, wait a while, and scrub with a nylon pad. It works well on turmeric and masala stains too.
